Various structures have been known for an offset fin used in a heat exchanger (see, for example, Unexamined Japanese Patent Publication No. 2008-39380). A structure of conventional offset fin 50 will be described with reference to FIG. 16.
Offset fin 50 is formed of a plurality of corrugation structures 60, 70. Each of corrugation structures 60 includes a plurality of fins 61 each having a protruding shape in cross-section. Each of corrugation structures 70 includes a plurality of fins 71 each having a protruding shape in cross-section. The plurality of corrugation structures 60, 70 are arranged in a direction orthogonal to flow direction D of a fluid. Corrugation structure 70 is disposed adjacent to and downstream of corrugation structure 60 in flow direction D.
Fins 61, 71 are each formed by bending a sheet of metal. Fins 61, 71 are each arranged to protrude in an upward direction in FIG. 16 at a constant pitch. Fins 61, 71 are arranged at an equal pitch. A position of fin 71 (a position in a direction in which the corrugation structures extend) is offset (disposed offset) from a position of fin 61.
Side walls 62, 72 of fins 61, 72 are parallel to a direction along flow direction D of a fluid, that is, flow direction D of a fluid. With offset fin 50 of this structure mounted to a heat exchanger, when a fluid flows in flow direction D, heat is transferred between side walls 62, 72 of fins 61, 71 and the fluid when the fluid passes through fins 61, 71. Turbulence occurs in the fluid because corrugation structure 70 is disposed offset from corrugation structure 60. An acceleration effect produced by the turbulence increases a heat transfer rate.